222 Beehy Thompson — Use of a Geological Datum. 



of the original record of the Kingsthorpe shaft becomes very 

 probable ; all difficulties of interpretation are removed ; and we 

 can give to the various formations their necessary thicknesses and 

 reasonable positions above O.D. 



The fact that in 1881 salt water filled the Kingsthorpe shaft to 

 within 270 feet of the surface is suggestive ; it would indicate that 

 the Marlstone rock-bed then determined the height to which the 

 water could rise, and, therefore, that salt water was then feeding 

 the Marlstone to some extent ; indeed, it is almost certain that, 

 according to the amount of pumping going on at Northampton, 

 the Kingsthorpe shaft may feed or be fed by Marlstone water. 

 Fortunately, the supply of salt water is very moderate, and the 

 greatest variation in chlorine I have observed in the Marlstone 

 water is 1-61 grains per gallon. In 1879, when Marlstone water 

 was used almost exclusively for the town supply, the water yielded 

 5-6 gi-ains of chlorine and 50*5 grains of solid matter per gallon; 

 in 1897, when it was used intermittently, the chlorine came out 

 as 3-99 grains per gallon, and solid matter 48. 



Before giving a revised section of the Kingsthorpe shaft, I must 

 justify another alteration to be made in the figures, etc. The Mining 

 Journal of September 3rd, 1854, in a description of the Kingsthorpe 

 undertaking, after giving an unintelligible classification of the beds 

 above, says that the Lias formation " was followed by 84 feet of 

 New Red Sandstone, 13 feet of Red Marl, and 15 feet of Con- 

 glomerate." This description was quoted in the 1854 prospectus 

 of "The Northampton Great Central Coal Mining Company." 



Mr. Sharp, in one place, says ' that the blue clay of the Lower Lias 

 was pierced at 860 feet, and is stated to have been succeeded by 

 80 feet of Sandstone, 12 feet of Red Marl, and 15 feet of Con- 

 glomerate; in another^ he says that at 880 feet the New Bed Sand- 

 stone was reached. My opinion is that all three descriptions are 

 essentially correct, and that the difference of 20 to 24 feet of beds, 

 which the geologists could not decide what to call, is the equivalent 

 of the Littoral Beds, 27 feet thick, above the Trias at the Kettering 

 Road boring, about which, and other beds below, Mr. Etheridge 

 said, "no equivalents in Britain," "no series like them" (Eunson, 

 p. 484). That these undefined beds at Kingsthorpe contained 

 conglomerates is evident, for in Miss Baker's collection of fossils 

 was a specimen of conglomerate consisting of limestone pebbles 

 in a greenish, sandy, and highly calcareous matrix, some parts 

 hard and crystalline, labelled " Top of Red Sandstone upwards of 

 900 feet, Kingsthorpe shaft," a label which until recently I could 

 not understand. 



In the revised section given below, the Upper Estuarine Beds, 

 Lower Estuarine Beds, and Ironstone Beds (not all ironstone, 



1 " The Oolites of Northamptonshire," part i : Quart. Journ. Geol. See, 

 March, 1870. 



2 " Note on a futile search for Coal near Northampton " : Geol. Mag., Vol. VIII 

 (1871), p. 605. 



